The present invention relates to a radio transmitter/receiver, or in particular to the QoS (Quality of Service) control of the transmission data in a radio transmitter/receiver.
In recent years, IP (internet protocol) has come to be employed for more and more networks with the extension of the internet and an inexpensive IP communication network. In the IP network, data are delivered to a destination from a transmitter in accordance with the IP. The IP is a protocol for a network layer (third layer) in the OSI reference model. Upper protocols include a TCP (transmission control protocol) and a UDP (user datagram protocol) in the transport (fourth) layer. The TCP and UDP have the function of acting as an intermediary between the IP and an application program. The protocols lower than IP, on the other hand, include those for a data link layer (second layer) and a physical layer (first layer). The Ethernet defined under IEEE802.3 and the radio LAN defined under IEEE802.11 are examples.
The radio LAN technique is used also for radio access to realize a subscriber network by radio, and various applications (including the WEB access, IP telephone and TV conference) have become possible to execute with the IP network in both a radio system and a wire system. Applications include those requiring the real-time operation such as video distribution and IP telephone, and those requiring no real-time operation such as the file data downloading.
In the IP network, on the other hand, in order to deliver time critical data such as the voice and video to the destination device within a predetermined time, the QoS control operation is used in which the transmission data are classified according to traffic type in the network and transferred by each node taking the QoS into consideration. The QoS control technique well known for the IP network includes, for example, MPLS or DiffServ at the network layer level and IEEE802.1D at the data link layer level.
The disclosure of IEEE802.1D is hereby incorporated by reference.
MPLS is described, for example, in “Multipleprotocol Label Switching Architecture” by E. Rosen et al., RFC3031, pp. 8-11, January 2001. DiffServ, on the other hand, is described, for example, in “An Architecture for Differentiated Services” by S. Blake et al., RFC2475, pp. 10-18, December 1998.
IEEE802.1D concerns a QoS control technique for the wire LAN, and implemented in such a manner that a priority indication label is attached to the header of the Ethernet frame, for example, and each bridge unit sets the transfer frames in a queue in the order of priority. According to IEEE802.1D, as shown in the priority classification of FIG. 13, for example, the traffic is divided into seven types 311 including “network control”, “voice”, “video”, “controlled load”, “excellent effort”, “best effort” and “background”, and the priority 312 is defined for each traffic type.
The “network control” is the traffic required for maintaining the network environment and handled with the highest priority “7”. The “voice” and “video” which are limited in delay time and jitters, on the other hand, have the next highest priority of “6” and “5”, respectively, following the network control. These traffic types are followed by the “controlled load”, the “excellent effort”, the “best effort” and the “background” in that order of priority. The priority of the normal LAN traffic including the mail and WEB are set in the category of “best effort”.
In radio communication, on the other hand, an adaptive modulation system has been proposed in which high-speed communication is established under satisfactory conditions of the radio section, while the communication rate is reduced in a deteriorated radio environment. Refer, for example, to “Symbol Rate and Modulation Level-Controlled Adaptive Modulation/TDMA/TDD System for High-Bit-Rate Wireless Data Transmission” by Toyoki Ue et al., IEEE Trans. on Vehicular Technology, Vol. 47, November 1998, the disclosure of which is hereby incorporated by reference, and JP-A-10-93650, JP-A-2002-290246 and JP-A-2002-199033.